1. Field of the Invention
The present invention relates to a technique of inspecting a pattern such as a wiring pattern formed on an inspected object such as a printed board or a film mask or a glass mask for preparing a printed board, and more particularly, it relates to a technique of displaying a reference image to be compared with an image of an inspected substrate.
2. Description of the Background Art
Generally proposed is a defect detector for detecting a defect in a wiring pattern or the like formed on the aforementioned inspected object (hereinafter referred to as “substrate”). This defect detector picks up an image (hereinafter referred to as “inspected image”) of a defective portion (defective area) of the inspected substrate with an imager such as a CCD camera and displays the image on a monitor. The defect detector also displays an image (hereinafter referred to as “master image”) of a reference master substrate similarly on the monitor. An operator of the conventional defect detector detects the defect of the inspected substrate on the basis of the inspected image with reference to the master image displayed in the aforementioned manner.
FIG. 21 illustrates an exemplary display of images on a display screen 100 of such a defect detector. Display areas 101 and 102 are set on the display screen 100 respectively. These display areas 101 and 102 display a master image and an inspected image respectively. As shown in FIG. 21, the conventional defect detector displays the reference master image and the inspected image respectively so that an operator can visually detect a defect. Further, the defect detector displays the inspected image at a display magnification identical to that for the master image, so that the operator can readily compare the two images with each other.
In an operation of detecting a defect of an inspected substrate, however, the operator may change the display magnification for the inspected image by operating an imager. In order to finely compare a circuit pattern of the inspected image with that of the master image, for example, the operator enlarges the inspected image displayed on the display area 102.
FIG. 22 illustrates the image (inspected image), displayed on the display area 102, enlarged by the operator. In this case, the conventional defect detector displays the master image and the inspected image at different display magnifications, and hence it is difficult to compare these images with each other and the working efficiency is disadvantageously reduced. Referring to FIG. 22, for example, the operator cannot determine whether a pattern 105 displayed on the display area 102 is to be compared with a pattern 103 or a pattern 104 displayed on the display area 101.
Also when the defect detector can change the display magnification for the master image, the operator must finely change the display magnification for the master image simultaneously with the operation of changing the display magnification for the inspected image, disadvantageously leading to reduction of the working efficiency.